The present invention relates generally to a clutch actuating device and, more particularly, to a clutch actuating device for use in a vehicle drivetrain subassembly.
Four-wheel drive systems for vehicles are being utilized to a greater extent, providing increased traction and safety of operation for the vehicle, particularly during inclement weather conditions or off highway conditions as compared to that provided by conventional two-wheel drive systems. Four-wheel drive systems typically include a torque transfer case which includes an input shaft connected to and driven by the output shaft of the main transmission, a rear output shaft connected to drive the rear wheels of the vehicle, a front output shaft connected to drive the front wheels of the vehicle, and means for drivingly connecting the input shaft to the front and rear output shafts.
In a known four-wheel drive system, characterized as a "part-time" system, a direct drive connection is provided between the front and rear output shafts of the transfer case when the vehicle is operated in a four-wheel drive mode. Such a direct drive connection does not permit the transfer case to accommodate different front and rear wheel speeds which can occur when turning the vehicle. Accordingly, the four-wheel drive mode is generally used only on a "part-time" basis, such as when lower friction road surface conditions, such as wet or snow covered pavement, may require increased traction capabilities. Consequently, the system may operate in either a two-wheel drive mode, a four-wheel drive mode or an "on-demand" four-wheel drive mode. A four-wheel drive clutch provides the direct drive connection between the front and rear output shafts of the transfer case. The four-wheel drive clutch is actuated using a rotary electric motor and an associated gear reduction mechanism which is required to provide the relatively high torque requirements necessary to bias the four-wheel drive clutch. While the aforementioned four-wheel drive clutch actuation system may be advantageously used in many applications, automotive design engineers are continually seeking to simplify, and consequently reduce the cost of, vehicle drivetrain systems.